50c black & green 'Presidente' issue with watermark and with diagonal 'OFICIAL' overprint in blue for use by the National and Congressional Libraries. A fine mint side marginal pair with variety OVERPRINT INVERTED and nice '9/2/28 L' marginal date inscription at right. Unrecorded. (Filatelia Chilena Catalogo Especializado # O43 variety, Unlisted by SG)